Ability to merge several jasper reports in one run

With added a possibility to merge several jasper reports programatically.

But with this ticket I found a way to implement it from the dictionary definition of the jasper field.

It is just to define several sources separated by ;

For example:

attachmentruebaOSGi.jasper;file:///opt/idempiere-server/reports/invoices.jrxml

This will combine the report PruebaOSGi.jasper obtained from attachment source with the report invoices.jrxml obtained from filesystem source.